Fisheries Stock Assessment: an inductive science with the Logical form of Primitive Magic

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Abstract. A logical analysis of the common fisheries models used in stock assessment has shown that they produce specific
predictions with the logical form of existential statements, fail Karl Popper’s falsifiability criterion, and so cannot be falsified
or tested by the empirical evidence. By contrast, the theoretical models of fisheries economics make predictions, not in the form
of existential statements, but in the form of universal patterns that exclude possibilities. These economic models meet Karl
Popper’s falsifiability criterion, since, from the logical point of view, the excluded possibilities represent potential falsifications
or tests of the model. Management decisions are presently guided by specific quantified predictions produced by those fisheries
models best supported by the facts or data; a pragmatic approach to prediction that involves an inference from past experience
and so makes the inductive assumption that we are entitled to argue from the past to the future. This inductive approach should
be replaced by a critical rational approach in which management decisions are based, not on those non-falsifiable
“metaphysical” models best supported by the facts, but on those falsifiable models that have been the best tested by the facts. A
critical rational thesis illustrated, in this paper, by the bold falsifiable Gordon-Schaefer model of fisheries economics, in which
bioenonomic optima (such as the maximum economic yield) are not interpreted in terms of specific quantified predictions but
are seen as “aims”or “ends” and interpreted as normative laws; norms that are indirectly incorporated into a social engineering
by way of the methodological rule of concomitance.